DE69619523T2 - Intrusion detection SYSTEM - Google Patents

Abstract

PCT No. PCT/GB96/01517 Sec. 371 Date Apr. 10, 1998 Sec. 102(e) Date Apr. 10, 1998 PCT Filed Jun. 24, 1996 PCT Pub. No. WO97/01160 PCT Pub. Date Jan. 9, 1997Vertical surface protection in a security installation is achieved by detecting disturbances in a microwave beam sent from a transmitter to a receiver, both installed substantially above the ground and adjacent to the vertical surface. The transmitter and receiver have associated beam aerials of extended horizontal aperture of not less than 0.50 meters (20 inches) to mitigate the effects of surface reflection from metal scaffold, plastic sheeting or netting, wooden boarding and brick or stone facing. The aerials are preferably slotted waveguide arrays and the advantages of using circular polarization are shown. Circularly-polarized slotted waveguide arrays are disclosed having a center feed to minimize frequency-dependent beam-spreading. The sensor may be used with an intruder detector to protect buildings in scaffold by utilizing triple technology exterior detection incorporating: microwave Doppler shift; at least one and preferably two passive infra-red devices linked together through timers and lens with horizontal curtain pattern; and anti-sabotage reflected active infra-red. The system can combine the aforementioned technologies into a new device and this format overcomes the individual limitations of each of the prior art technologies when used in unison in an external scaffold environment.

Description

The invention relates to intrusion detection systems and components therefor. It particularly relates to intrusion sensors and intruder detectors for use in protecting vertical surfaces.

The term "vertical surface" refers to an actual or imaginary surface that is vertical in its main component and is not necessarily a flat surface. In particular, the vertical surface can be a surface of a building or an imaginary surface that is determined by the surface of a scaffold or a scaffold tower. A horizontal plane or surface should therefore include all surfaces that are essentially perpendicular to such a vertical surface.

According to one aspect of the invention there is provided a method of installing an intruder alarm system which enables detection of an intruder climbing through a zone to be protected, the method comprising installing on opposite sides of the zone a microwave transmitter having an associated microwave antenna and a microwave receiver having an associated microwave antenna, the receiver being adapted to receive radiation transmitted by the transmitter, the receiver having means responsive to variation in the received radiation outside a predetermined range for generating a signal indicative of the presence of an intruder in the zone between the antennas, the transmitter and receiver antennas each having an aperture which is not less than 0.50 metres (20 inches) in a direction substantially perpendicular to a vertical surface, the method further comprising mounting the antennas proximate the vertical surface on opposite sides of the zone to be monitored for the presence of an intruder such that a microwave beam pattern between the antennas forms a detection field, which is located in a substantially horizontal surface that is oriented so that the system can detect an intruder climbing through the zone.

In a preferred method, each antenna is provided by a horizontal array of radiating elements that cooperate to provide the required horizontal beam pattern. The beam pattern preferably has a half-power beamwidth of no more than 2 degrees.

It is desirable that each of the antennas include an array of radiating elements extending in a horizontal plane and cooperating to provide a substantially horizontal beam pattern having a beam width at half maximum of no more than 2 degrees. The antennas are mounted in spaced relation near the vertical surface so that each element of the receiver array receives radiation components directly from each element of the transmitter array, together with components reflected from the vertical surface from at least some elements of the transmitter array. The direct components and the area components at the receiver antenna add vectorially.

Possible antenna components for use in these aspects of the invention are already disclosed in UK-1475111, which is comparable to US-4,079,361. This patent describes the conventional form of microwave beam sensor in which the important reduction of ground reflection is already incorporated. The antenna elements have been designed with the aim of reducing ground sensitivity. This is to avoid problems with false alarms caused by moving and growing plants, etc.

Conventional microwave transmitters and receivers are designed to be mounted vertically above the ground and have beam antennas with an extended vertical aperture of at least 0.75 meters (30 inches) to minimize the effects ground reflection. The preferred vertical antennas consisted of a slotted waveguide arrangement with circular polarization to keep the beam spread as small as possible.

However, studies have shown that while the sensitivity to ground reflection components decreases, the suitability of the sensor decreases. An intruder who walks, runs or crawls will be detected, but an intruder who crouches down and makes his body cross-sectional area as small as possible will generally not be detected. Despite this difficulty, the system can be adapted for use in the invention without this problem occurring.

Preferred installation methods that take into account the above aspects of the invention can be developed as follows. Take the conventional intruder sensor with reduced sensitivity to ground reflections and mount it not vertically as intended but in a horizontal plane with both the transmitter and receiver rotated 90 degrees and raised from the ground and placed to protect a vertical surface or side, e.g. of scaffolding. The reduced sensitivity at the surface edge of the detection field is no longer a disadvantage since the intruder is now climbing and cannot ascend vertically undetected. It is impossible for the intruder to reduce his body cross-sectional area while climbing as he can while crouching on the ground.

In real situations, microwave fences can be built on irregular scaffolding arrangements and/or scaffolding surfaces that are outdoors and covered with plastic sheets or nets. At microwave frequencies, scaffolding sheets and nets affect the reflection and thus lead to changes in the actual surface level. Short-term changes can be caused by plastic sheets or nets, moving in the wind. Since the antennas now operate horizontally, the effects of surface reflections from the scaffolding surface, wooden boards and plastic sheets or nets are mitigated. This reduces the problems caused by false alarms or no alarms being triggered and provides a more predictable and reliable behavior of the microwave sensor system.

In horizontal mode, the minimized beam expansion is a significant advantage, as vehicles and pedestrians can drive or walk under and behind the detection field.

It has generally been assumed that the sensitivity of the microwave system mentioned is set so that birds and small animals entering the detection pattern do not cause interference with the received signal sufficient for detection. Tests have shown that a bird or small animal within 0.5 to 1.0 meters of the transmitter or receiver antenna can very well trigger an alarm condition. Similar conditions can be created within the one-meter area of the transmitter or receiver antenna by melting ice, melting fallen snow or heavy (tropical) rain on the radome front.

A preferred installation method according to the invention eliminates all of the above failures by moving a part of the radome structure forward from the horizontal transmitter and receiver antennas by a distance of at least 0.5 meters, e.g. 1.0 meter.

The beam pattern or fence must be designed to have a sufficient horizontal width that it is difficult for an intruder to bypass. The smallest possible fence width is determined by the horizontal openings of the antennas, taking into account that the fence widens horizontally the further away from the antennas due to beam divergence. For increased security, it is preferable to have a horizontal opening larger than that mentioned, for example 1.50 metres, but one does not normally make the fence width so large that the movement of an intruder through the fence causes insufficient change in the received signal to enable an intruder to be reliably detected.

As in US-4,079,361, a beamforming antenna enables the effects of surface reflections to be at least greatly mitigated. The best performance is achieved when the angle of incidence α of the reflected beam path on the vertical surface between the transmitter and receiver antennas is not less than half the half-power beamwidth (θ) of each array, i.e. α

θ/2. This ensures that the reflected beam path is outside the radiation pattern of the antennas (location of the 3dB drop). α depends on both the distance between the antennas and the horizontal extension of the antennas. α decreases with distance and increases with horizontal extension. Thus, with sufficient spacing, α can eventually fall below θ/2. However, US-4,079,361 shows how to use the antennas in such a way that the distance at which this occurs is outside the practically relevant ranges. Increasing α by increasing the horizontal extension does not achieve the goal, since for a practically feasible fence it is necessary that the fence tightly encloses the vertical area. US-4,079,361 shows how antennas containing a horizontal radiator array can be used on or near the vertical surface without causing difficulties with surface reflection. It suggests that such arrays should probably have a horizontal beam width at half maximum of no more than 2 degrees.

The desired beam widths can be easily achieved with horizontal apertures of the size proposed for the X and K bands. For example, a horizontal aperture of 1.50 meters in the X band produces a horizontal Half-power beamwidth of less than 1 degree. The same aperture produces half the beamwidth in K-band; the same beamwidth can be achieved with a 0.75 meter wide array.

It can be seen that in the X or K band (λ = 0.03 or 0.015 meters) the antenna aperture is very large in relation to the number of wavelengths and that very narrow beam heights can be achieved, with the fence widths being those desired in practice.

When considering the beamwidths achievable at microwave frequencies in the horizontal direction, it should be noted that the physical width of the antenna aperture is related to the beamwidth. Regarding the surface reflection problem from the horizontal beam pattern of the antennas, a beamwidth of no more than 2 degrees is considered desirable.

It is preferred that the beam forming antennas used in a sensor according to the above aspects of the invention are circularly polarized. Such antennas make the sensor less sensitive to the direction of an intruder, e.g. a man climbing or crawling vertically. This occurs more easily with linearly polarized antennas and the use of circular polarization can also be advantageous in distinguishing vehicle reflections. This factor may play a role in certain locations where a fence is erected. A slotted waveguide arrangement is particularly well suited for this purpose.

To monitor the level of the received signal, it is preferred to modulate the transmitter and monitor the level of the detected modulation in the receiver. In addition, one wants to make provisions to compensate for long-term changes in the received signal level.

A complete intrusion detection system can be created with one or more such sensors. For example, if a building is completely scaffolded, a combination of four or more sensors may be sufficient if they are arranged to protect against frontal entry in an upward direction. However, a single such sensor may be sufficient to detect intruders climbing vertically downwards, i.e. from a roof onto the scaffolding. Two such sensors next to each other can adequately protect certain scaffolding structures, not only against frontal access but also from side access.

In many scaffolding arrangements, the distance to be protected laterally is less than 10 meters. In contrast, the sensors described above are generally more effective at distances between 10 and 150 meters.

Thus, according to a second aspect of the invention, there is provided a method of installing an intruder alarm system enabling detection of an intruder climbing through a zone to be protected, the method comprising installing first and second passive infrared devices, each device providing a set of detection pattern segments defining a first curtain and a second curtain respectively such that their respective curtains extend across the zone monitored for the presence of intruders, each along vertically spaced, substantially horizontal planes, the system further comprising means responsive to the passive infrared devices, the responsive means including storing timer means storing the time at which an intrusion into one of the curtains is detected by the associated passive infrared device and operable to generate an alarm condition signal if an intrusion into the other of the curtains is detected by the other associated passive infrared device before a given time interval has elapsed since the time of the first-mentioned intrusion.

Preferably, a microwave transceiver is attached to one or both of the infrared devices, the microwave transceiver having a detection pattern that overlaps the curtain of at least one infrared device or is at least coextensive.

According to a third aspect of the invention there is provided a method of installing an intruder alarm system that enables the detection of an intruder climbing through a zone to be protected, the method comprising installing:

a passive infrared device providing a set of detection pattern segments defining a curtain, the device being installed so that the curtain extends along a substantially horizontal plane;

a microwave transceiver attached to the infrared device such that a detection pattern of the transceiver overlaps the infrared curtain or at least has substantially the same extent; and

an active alignment device comprising a transceiver containing a transmitter that transmits an alignment beam and a receiver that detects a reflected component of the alignment beam, and the active alignment device is physically attached to either the microwave transceiver or the passive infrared device such that if the passive infrared device or the microwave transceiver is misaligned, the alignment beam will no longer be reflected back to the receiver of the active alignment device, thereby providing a safeguard against masking and intentional misalignment.

The infrared device or devices may be operated to provide a protective curtain, e.g. by requiring disturbance in three consecutive patterns at a given speed. The microwave device, if present, may be designed to generate an alarm only if it and the infrared device together indicate an intruder within a given time period, e.g. 15 seconds or less.

Preferably, there is a third protective device in the form of means physically attached to the devices that detect tampering, such as the removal or simply moving of the devices.

This aspect of the invention is based on research into protecting scaffold areas less than 10 meters (33 feet) in length. The operating range of the preferred embodiments extends from 0.50 meters (1.6 feet) to 15 meters (50 feet). The detector can be designed to meet the desire for protecting scaffold ends, cranes, hoists, scaffold towers and other scaffold lengths less than about 10 meters (33 feet).

The device can be installed independently or, if necessary, complement the sensor according to the previous aspects.

There are two or three conventional technologies, disclosed for example in US-4,079,361, EP-A-0499177 and EP-A-0337964, which allow detection of intruders. The fusion of these combined technologies into a device installed according to the methods of the invention provides at least one or preferably two horizontal infrared curtains optionally in conjunction with a microwave transceiver having an at least partially overlapping detection pattern and meets stringent criteria for intrusion detection systems protecting scaffolded buildings. A preferred method is based on the use of a system, which uses a curtain cover, particularly for shorter scaffolds. This means that an array of segments can be provided, e.g. two horizontal infrared curtains (spaced vertically, for example, 30 to 100 centimeters apart) or such a curtain in conjunction with a partially overlapping microwave field. It is easy to arrange pairs of curtains, one above scaffold boards, etc. and the other below. This arrangement means that birds and other animals sitting or walking on these boards do not disturb the detector.

The preferred method is to use a triple technology external detector comprising: an unobscurable microwave Doppler shift; two unobscurable passive infrared detectors with latching timers and curtain pattern lenses; and tamper resistant reflective active infrared devices. Using these methods individually does not satisfy the requirements; the reasons for this are explained later in this patent.

The preferred method of the invention includes the technologies mentioned. Thus mounted on a scaffold according to the claimed method, the limitations of each individual conventional device are eliminated as follows.

The Doppler microwave detection pattern and a special passive infrared curtain detection pattern contain one or more curtains and are preferably identical up to a maximum distance of, for example, approximately 15 meters (50 feet). If the pattern range is to be changed to suit the specific requirements of the location, the Doppler distance range is continuously adjustable. The passive infrared unit or units do not have an arbitrarily finely adjustable distance range in their detection patterns. In this embodiment, the length only in fixed patterns by changing the lenses or mirror segments. This is not considered a practical proposal for variable length gantry systems. If both sensing devices are deployed together, the passive infrared pattern area outside the microwave transceiver is erased. To generate an alarm condition, both the microwave and infrared devices are triggered within a given time period, e.g. within 10 to 15 seconds of each other.

The inherent sources of error of an external infrared detector, i.e. direct or reflected sunlight, wind chill, rapid temperature changes of neighboring objects, and changing detection patterns with a change in external temperature, are eliminated by the stability of the microwave detector, which is not affected by these failures.

Similarly, the infrared stabilizes the inherent weaknesses of the external microwave transceiver, i.e. heavy rain, hail, snow, vibrations, fluorescent lighting, plastic water pipes, swinging ropes and the ability to penetrate glass and thin partitions.

The shortcomings of the two technologies cancel each other out, with the exception of false alarms caused by birds, cats and small animals in close proximity to the detectors. In addition, the two technologies can be misaligned when the system is disarmed, without turning the scaffold post to which the device is attached triggering an alarm condition.

The preferred installation method of the invention eliminates the above-mentioned difficulties. The problem of false alarms caused by birds, cats and small animals can be solved by installing two curtain lenses from two anti-mask passive infrared detectors in addition to the latching timers to the infrared detectors. The two curtain infrared detectors are mounted horizontally, preferably 30 centimeters to 100 centimeters (12 to 39 inches) apart, and they are mounted elevated on the outside of the scaffold, preferably by at least 50 centimeters (20 inches), most preferably at about the height of the first boarded (or unboarded) level, which is typically about 2 meters (six feet six inches) above ground level. In this mode, the double curtain masking pattern, together with a single pre-trigger operation in conjunction with latching timers, detects only one climbing intruder and does not cause false alarms. An alarm condition occurs when the climbing intruder passes through both curtains of the detection pattern within a variable time limit. The two horizontal detection patterns and the arrangement on the outside of the gantry reduce false alarms caused by landing or taking off birds or jumping small animals whose path crosses the curtain detection pattern, and due to their speed they only trigger the pre-trigger and thus avoid false alarms.

The installation of the two curtain lenses on the outside of the scaffolding also allows birds and small animals to move freely on the boards and horizontal bars of the scaffolding without being detected.

To avoid masking and intentional misalignment of the detector when the system is powered down, a reflective active infrared beam transceiver is incorporated into the device. This transceiver, itself essentially constructed using conventional technology, transmits an active infrared beam to a reflector. The reflector directs the signal back to the transceiver, creating a continuous path. The transceiver and reflector are arranged to provide the approximate Represent the center line and length of the detection field. If the device is intentionally misaligned when disarmed, the infrared beam will no longer be reflected and a warning signal will be given. If intentional sabotage occurs, ie the detector is covered by objects placed in front of it, the reflected infrared path will again be interrupted and an alarm condition will occur.

The deficiencies of the active infrared beam unit described below are not present in the device for the following reasons. The infrared component is used only for alignment checking and not for intruder detection. Thus, the inherent narrow beam deficiencies are of little importance in this application. Optical alignment between conventional transmitters and receivers and the difficulties that result from this are eliminated by the single beam of the reflector. The reflected beam produced by the transceiver greatly reduces the need to precisely align the single beam between transmitter and receiver. Thus, the reflected path provides a less precise but reliable signal pattern for a maximum of 15 meters (50 feet). The reflector and transceiver can be protected by conventional 24/7 anti-tamper circuitry. The circuit can protect the mechanical fastenings and prevent the devices from being moved with the intent to commit crimes.

It is intended to disconnect the active infrared alignment circuit when the monitoring system is disarmed to allow authorized personnel to enter the scaffold. The alignment circuit is reconnected when a test circuit in the monitoring system is activated. The alignment test circuit is automatically activated during arming of the system. If no misalignment or obstruction of the infrared beam has occurred, the the system automatically starts operating. If misalignment or coverage has occurred, the alignment circuit remains open, preventing the control device from making adjustments and informing authorized personnel of the situation.

The test circuit can always be activated when the system is disarmed, i.e. after a scaffolding conversion, etc. If a communication link is installed, a central monitoring station operating around the clock can remotely activate the alignment test circuit when required.

When the system is armed, the alignment circuit will remain in operation. An alarm condition will not be generated until the circuit is activated for at least 10 to 20 seconds, indicating coverage or misalignment. Continuous blocking of the active infrared beam for more than 10 to 20 seconds will generate a full alarm condition. The allowable variable time period is not affected by birds or small animals flying or jumping through the infrared beam pattern.

The three devices are to be mounted together with their own boom rods and clamps in a robust waterproof plastic housing. The internal mechanical fixings are fully enclosed. The housing is protected by a 24/7 tamper protection circuit.

For a better understanding and to show how the method of the invention may be carried out, it will now be described by way of example with reference to the accompanying drawings.

It shows:

Fig. 1 conventional active infrared beam units with narrow beam detection according to the state of the art;

Fig. 2 conventional passive infrared detection systems according to the state of the art;

Fig. 3 shows conventional microwave detection patterns according to the prior art;

Fig. 4 conventional prior art microwave detection patterns in contact with scaffolding posts, boards, tarpaulins, etc., reflecting and producing cancellations and antiphase signals leading to false alarms and unstable conditions;

Fig. 5 and 6 show conventional microwave detection patterns according to the state of the art that allow an intruder "free space" in Fig. 5, or in Fig. 6 microwave detection patterns with at least 10 meters of available rectangular gantry length with a 3 meter (10 foot) boom;

Fig. 7 is a schematic block diagram of the installation and components that meet the described requirements for a wired system;

Fig. 8 is a schematic block diagram of the installation and components that meet the described requirements for a wireless system with radio frequency signaling;

Fig. 9 and 10 show in plan and front view an example of two different detectors, referred to here as intrusion sensor and intruder detector, for use in the systems of Fig. 7 and 8;

Fig. 11 shows in perspective the use of the detectors in Fig. 9 and 10 to protect the front surfaces, sides and top level of a boarded scaffold;

Fig. 12 the invisible energy field in the system according to Fig. 11;

Fig. 13 and 14 show two alternative arrangements and deployment of the two detectors covering all sides, surfaces, corners or internal voids of the unplanked scaffolding;

Fig. 15 is a plan view of an intrusion sensor;

Fig. 16 is a block diagram of the circuit of the intrusion sensor system;

Fig. 17 is a simplified perspective view of an antenna arrangement usable in the system of Figs. 15 and 16 and providing circular polarization;

Fig. 18 is a simplified front view of another antenna arrangement providing circular polarization and usable in the system of Figs. 15 and 16;

Fig. 19 shows a modification of the slotted waveguide arrangement in Fig. 17 with reduced beam expansion;

Fig. 20 a reflector system;

Figs. 21 and 22 show the detection patterns obtained with an intruder detector for a standard lens pattern and a narrower width arrangement obtained by rotating the lower and upper lenses in opposite directions;

Fig. 23 an intruder detector individually mounted on a scaffold side surface;

Fig. 24 Intruder detectors individually mounted on a scaffold tower, covering the front and side surfaces;

Fig. 25 an active infrared beam designed to prevent masking and misalignment; and

Fig. 26 is a block diagram of a detection circuit of an intruder detector.

First, let us consider conventional systems that are attached to external scaffolding for protection, see Fig. 1 to 6.

Conventional active infrared beam units

1. Ordinary single-beam, dual-beam or multi-beam units, see Fig. 1, provide only a narrow protective beam line 1, which can easily be avoided with the help of night vision devices (the beam is visible and can be avoided).

2. Such devices can also be easily circumvented because the transmitters and receivers are visible and thus indicate the line of the protected area. The active infrared beam 1 between the transmitter and receiver housing is extremely narrow and does not cover any volume, so that a climbing intruder can easily avoid it. Since the beam is narrow, it must be placed close to the front of the scaffold, thus giving the intruder the opportunity to climb over the enclosure undetected.

3. Active infrared rays do not work satisfactorily at less than 8 meters (26 feet), so they are not suitable for protecting the ends of scaffolds, towers, cranes, hoists, etc.

4. Infrared rays can be adversely affected by heavy rain, fog, snow and vehicle exhaust fumes. The devices are not designed to withstand the harsh scaffolding environment.

5. Active infrared devices are optically aligned to operate and the units are designed to be permanently mounted to a rigid structure. If they are attached to a temporary scaffolding arrangement, the narrow active infrared beam can wander out of optical alignment and cause malfunction. Alignment instabilities caused by traffic and working vibrations of the scaffolding are also problematic.

Conventional external passive infrared detectors (P.I.R.)

1. The standard lens coverage field of a P.I.R., see Fig. 2, operates up to a defined distance, both in a volume pattern and in a long-distance pattern. The devices do not have a finely adjustable distance limit to adapt to individual scaffold dimensions. Often the coverage pattern is either too large or insufficient for the requirements.

2. Passive infrared detectors are adversely affected by direct or reflected sunlight, wind chill effects and rapid temperature changes from neighboring objects, causing false alarms. The detection field changes as the ambient temperature changes. This can cause false alarms to be generated by pedestrians and traffic under the scaffold.

3. Passive infrared detectors are also prone to false alarms caused by birds and small animals, especially when very close to the device. This often happens if the detection pattern covers the boards and poles of the scaffolding.

4. An external detector can easily be sabotaged by covering or misaligning it, both when armed and when off, without generating an alarm condition.

Conventional microwave Doppler shift transceivers

1. Standard microwave transmitters and receivers (radar) are used to provide a variable volume detection pattern. The receiver operates on the principle of the Doppler-shifted (reflected) signal emanating from the moving intruder. This principle gives satisfactory results indoors, but is unreliable in an open environment. The reflected signal can be disturbed by heavy rain, hail, snow, vibrations, fluorescent lights, plastic water pipes, swinging ropes, birds and small animals in close proximity to the detector and the ability to penetrate glass and thin partitions, and can produce false alarms.

2. An external detector can easily be sabotaged by covering it or misaligning it when it is turned off, without generating an alarm condition.

Conventional electronic vibration sensors, microphone wires and geophone sensors against intruders

1. Standard sensor systems are unreliable when used on an external scaffold. To detect an intruder climbing the scaffold or walking on the scaffold boards, one must set the sensitivity of a standard vibration detector to almost the highest possible level. This leads to false alarms caused by resonance and vibration from passing vehicles, blaring sirens (emergency vehicles), closely spaced plant and machinery, and pedestrians knocking on the scaffold below.

2. Similarly unsatisfactory results are obtained with microphone wires and geophone sensors.

Acoustic detection devices

1. Conventional acoustic (audio) detectors are not suitable for use in a scaffolding environment as they cannot distinguish between the sounds caused by intruders and the tangle of disturbing ambient noise from trains, road traffic, nearby equipment and machinery, passers-by, etc.

Electrostatic field wire system

1. The standard system is triggered when a person is in close proximity to the wire arrangement containing the detection field. The device is adversely affected by the close proximity of the metal framework. If the parallel wires are removed from the framework surface, they are exposed to entanglement with ladders, hoists and ropes and breakage. False alarms are very common.

Conventional microwave beam detectors

1. Standard external microwave beam detectors, see Figs. 3 to 6, do not work satisfactorily when mounted on scaffolds because the beam width cannot be controlled. This leads to false alarms from passing vehicles entering the beam side maxima and from pedestrians and traffic under the scaffold. For example, for a scaffold length between 30 meters (90 feet) and 100 meters (330 feet), the average diameter of the microwave detection beam is 6 meters (20 feet). This is not acceptable on the outside of boarded scaffolds (see Fig. 3).

2. The sensitivity of the detection beam is uniform over its circumference and length. When the signal comes into contact with scaffolding posts 4, boards 5, tarpaulins 3, etc., it is reflected and produces cancellations and antiphase signals. These unstable conditions are likely to create unprotected areas and false alarms (see Fig. 4).

3. Due to the signal pattern close to the transmitter and receiver, an empty area exists which provides an "clearance" 6 (Fig. 5) for the intruder to climb the scaffold undetected. This feature is a disadvantage common to all standard microwave detectors and can only be minimized if a scaffold length of 10 meters (33 feet) or more at right angles is available, so that a second pair of transmitters and receivers with a crossed signal pattern can be installed to cover the empty area (see Fig. 6).

4. Most scaffold ends are only about 2 meters wide. This means that a second set of detectors cannot be used, and leaves an unprotected area of the scaffold that the intruder can enter.

5. Should additional safeguards in the form of a second pair of transmitters and receivers be installed in parallel with the external microwave detectors in an attempt to protect the vulnerable windows and board areas of the scaffold, this will not solve the problem. The detection signal pattern will be adversely affected, reduced and "channelled" through the framework of the scaffolding rods 4. The sensitivity of the detection signal is uniform over the circumference and length of the signal pattern, causing cancellations and anti-phase regions on at least two areas of the signal pattern. This mode will cause false alarms and instabilities as environmental conditions change.

6. Another disadvantage of using standard microwave detectors, especially when mounted on scaffolding in front of a building with glass fronts or large windows, is that you cannot control the width of the signal field to prevent the signal from penetrating the building through the glass and interfering with electronic office machines, radio frequency equipment, etc.

7. All standard microwave detectors will ignore birds and small animals for most signal patterns if the sensitivity level is set correctly. The standard detectors will give an alarm if a bird in slow flight to land and enters the signal pattern within 1.0 meters of the transmitter or receiver. If a standard microwave device is installed in a scaffold, the number of birds landing or flying off the scaffold in the vicinity of the detectors increases dramatically. The probability of false alarms is therefore high.

8. Standard microwave detectors can generally only be installed on scaffolding that is longer than 10 to 200 meters. If installed on scaffolding that is less than 10 meters, the signal is unstable and cannot be scaled down sufficiently to work reliably. This excludes most scaffolding towers, hoists, cranes, private townhouses and shop fronts, which are usually less than 10 meters wide.

Various systems and installation methods are now proposed with reference to Figs. 7 to 14, whereby the devices referred to here as intrusion sensor and intruder detector are used alone or together. The systems and installation methods in Figs. 7 to 12 use both devices. In contrast, in Figs. 13 and 14 only one device is used.

The overall systems shown in Fig. 7 and 8 are designed according to the following requirement:

System installation requirements

1. The scaffold must be flooded with a controlled energy field. Only intruders with a mass of more than 25 kilograms and/or vertically climbing intruders may be detected.

2. An intruder shall be detected attempting to climb the outside, corners or sides of a boarded scaffold erected as shown in Fig. 12. An intruder shall be detected attempting to climb the side of the scaffold facing a building if access is possible.

3. An intruder must be detected climbing any side, surface or corner or climbing through an unboarded scaffold (see Fig. 13).

4. A human intruder must be detected before reaching the first scaffold level or the first window row above ground level penetrated by the scaffold (or other heights near roofs etc. to be protected if necessary, see Fig. 11).

5. The detection system must not be triggered by pedestrians or vehicles under or behind the sides of the protected scaffold. The detection field must not penetrate windows or interfere with office machines in the building.

6. The primary protection of the detection system is to provide an invisible wall of energy from 0.5 meters (1.6 feet) up to 150 meters (500 feet) in length.

7. The width and height of the protective energy field must not be determinable or surmountable by an intruder.

8. If an intruder attempts to enter the protected area, a siren and a pulsating flashing light will immediately sound for a predetermined period of time, usually one to three minutes. The siren will then stop and the system will automatically re-arm.

9. Option: If necessary, the system can also switch on headlights. If headlights are permanently on in the dark, the system will pulse the headlights when the alarm is triggered.

10. Option: If required, all events in the system can be transmitted via a communication link to a central monitoring station operating around the clock.

11. Option: If required, the system can be supplemented with alarm photo evidence cameras that survey the detection area. If an intruder enters the protected area, the detectors activate the infrared flash units of the photo evidence cameras and record a number of individual images. The images are transmitted within 15 seconds, together with the standard signal for an intrusion event, to the 24-hour alarm system. central monitoring station. If required, the detectors can be connected to a CCTV system for monitoring, recording or transmission.

1. Requirements for the external system and procedure

1. The detection devices shall be mounted in robust weatherproof plastic enclosures, which shall have their own cantilever scaffold poles and clamps. They shall be mounted at each end outside the main scaffold structure. This shall provide the greatest possible detection area for the energy field along and through the scaffold together with the lowest risk of accidental damage from the site environment. The plastic enclosures shall be sealed to prevent water, dust, insects etc. from entering the unit.

2. The energy detection field must not be affected by vibration, wind, falling leaves, flying dirt, dust, rain, hail, fog, frost, ice, snow, sunlight or extreme temperatures.

3. The energy detection field does not respond to birds and small animals.

4. The energy collection field is stable and is not affected by metal parts of the scaffold, the scaffold debris nets, the canvas tarps, the polyethylene cover and the scaffold wood boards.

5. The electromagnetic radiation and frequency meet the requirements of the D.T.I. (UK), F.C.C. (USA) and, if necessary, other countries.

6. The detection and the associated electronics are not affected by high-pitched siren sounds and portable high-frequency transmitters, i.e. by fire brigade, police, rescue services, mobile phones, etc.

7. The detectors and devices are shielded to suppress radio frequency interference. The wiring is fully shielded if necessary.

8. All electrical voltages applied by internal control units to detectors and sirens are reduced to a maximum of 24 volts DC to ensure that they do not Health & Safety at Work Acts and Codes of Practice as they relate to scaffolding. The detectors are earthed to the scaffolding poles, which in turn are earthed to the main scaffolding structures.

9. To prevent deliberate tampering, the detectors are protected against covering to maintain a consistent detection pattern throughout the installation period. During the workday, when the system is off, any deliberate tampering caused by mechanical misalignment of the detectors or placing large objects in front of the detectors will be indicated on the control panel. The indicated tamper area and the system will not arm until a 24/7 technician realigns the system to ensure that the protected area is accurately covered. If mechanical misalignment occurs when the system is armed, a full alarm condition is immediately generated.

10. A separate anti-tampering circuit, operating around the clock, protects against tampering with cables, housings, control devices, etc. If any of the anti-tampering circuits mentioned are activated, an acoustic and visual tampering alarm (indicating the location) must appear on the internal control panel. If an optional communication link is connected, a tampering signal (sabotage signal) is sent to the central monitoring station, which notifies the 24-hour technical on-call service and authorized authorities.

11. External sirens and flashing lights shall be housed in strong polycarbonate casings and secured to the scaffold. When the system is shut down during daily operations, the siren shall be activated, powered by its own internal battery, in the event of any attempt to cut the siren cable or tamper with the casing. The siren and flashing light unit shall be clearly marked as "electronic scaffold protection" to avoid confusion with other alarm sirens that may be sounding in the vicinity.

12. Option: If access to the internal control device is not available, an external digital keypad is provided in a damage-proof, weatherproof and lockable housing, which enables the system to be armed and disarmed without having to enter the building. The external digital keypad must be backlit for night-time operation, must be able to query the event log and be protected by the 24/7 tamper protection circuit.

13. Option: If required, the detectors are connected to the intruder photo evidence cameras that monitor the detection field. When an intruder enters the protected area, the detectors activate the infrared flash units to record a number of individual images. Detector interfaces are also available for a complete CCTV camera system.

1. Requirements for the internal system and procedure

1. All control and communication equipment shall be assembled and mounted to form a free-standing portable appliance. A Certificate of Inspection shall be provided to show compliance with the Electricity at Work Act. The control equipment shall be located in a secure area of the building, site office or security hut.

2. The system is armed and disarmed using a digital keypad located in the main control unit. The control unit indicates the area of the scaffolding that is being breached by an intruder and activates an internal sounder (with adjustable volume). The audible internal sounder will activate if any detector, siren, cable or control device is tampered with, regardless of whether the system is armed or disarmed (24/7). The exact location of the tampering is indicated.

3. If an alarm is triggered, the internal control system immediately alerts a porter who is available around the clock, security personnel, key holders, police authorities, etc. If necessary, the notification of an intruder in the protected area is immediately transmitted electronically via a high frequency radio paging system, a digital telephone communication link or a mobile phone data link.

4. All events on the system are also recorded in the control device located in the building or the site office and displayed on a liquid crystal display or printed on a real-time printer.

The following events must be displayed:

Time, date and location of an attempted intrusion on the scaffolding;

Time, date and name of the person who armed or disarmed the system;

the digital keyboard the person used (internal or external);

whether the authorized person who armed the system intentionally bypassed (bypassed) any part of the system, and which parts of the system were bypassed;

Time, date and location of any manipulation (sabotage) of detectors, cables, control devices, etc. regardless of whether the system is armed or switched off (all day);

Time and date of a power outage; and

the failure of the telephone line.

5. The system has rechargeable emergency power batteries in case of a power failure. The system must be able to operate normally for 24 hours. In the event of a prolonged power failure, an audible and visible warning is given. If a communication link is connected, a signal is sent to the central monitoring station to alert the 24-hour technical emergency service and the authorized authorities.

Option 6: Remote signaling of an intruder in the protected area is received within 10 to 15 seconds by a British Standard Central Monitoring Station. The 24-hour staff immediately alerts private security services, Doormen, authorized residents, key holders, neighborhood watch, police authorities. If the building is secured with an interior alarm system, personnel must also notify the internal alarm monitoring station to be ready. If the interior alarm is subsequently triggered, the police can be informed that an external scaffold alarm was followed by an internal building alarm (secure verification). If necessary, the 24-hour key holding or alarm reset service must be notified. All event signals and actions taken including "building open", "building closed", "intruder", time of day and "tampering/sabotage" are recorded in the central monitoring station. In the event of a prolonged power outage, "dead emergency battery" is also recorded. An event signal is also recorded if the authorized person arming the system intentionally omits (bypasses) any part of the system. The cellular data connection is also monitored to check the device on site and cellular transmission and reception.

Option 7: When external detectors are installed together with an intruder photo evidence system, the central monitoring station receives a number of individual images on the computer screen via the communication link. This occurs simultaneously with the normal intruder event signal. All events or photos received and actions taken are recorded and can be distributed as a hard copy or in electronic formats. A system interface is provided for full CCTV system monitoring, recording or transmission.

8. Option: The on-site control device facilitates computer access to the storage unit (downloading) from the central monitoring station via the communication link. The functions can be remotely analyzed, checked and reprogrammed by authorized personnel if necessary.

Two new detectors have been invented to eliminate all of the described operational limitations of conventional external intruder detection devices when mounted on a scaffold. These detectors can be designed to meet the requirements and eliminate the limitations of the conventional devices. The following are example lists of components, see Figs. 7 and 8, for installation according to the method of the invention to meet the requirements.

WIRED SYSTEM External devices (wired) (see Fig. 7)

1. Intrusion Sensor 7 with a detection range of 10 meters (33 feet) to 150 meters (500 feet).

2. Intruder detector 8 with a detection range from 0.5 meters (1.6 feet) to 15 meters (50 feet).

3. Siren and flashing light unit 9.

4. Warning signs (standard equipment).

5. Eight-core safety cable 11 (standard equipment).

6. Option: Intruder photo evidence cameras 10 complete with an infrared flash unit connected to the detectors and sensors.

7. Option: CCTV camera 12 connected to the detectors (standard equipment).

Internal control equipment (wired) (see Fig. 7)

1. Control panel 13, expandable to fifteen areas and equipped with a memory computer from which 1000 events can be downloaded, an output for real-time printing and alphanumeric paging.

2. Digital LCD keyboard 15, which is backlit .

3. Power supply unit 16 with 12 volt and 24 volt DC voltage, which contains rechargeable emergency batteries.

4. Assembly unit for the control equipment to form a free-standing portable device 17 (itself a new invention).

5. Option: Real-time printer 14.

HIGH FREQUENCY SIGNALIZATION (WIRELESS SYSTEM) External devices (wireless) (See Fig. 8)

1. Intrusion Sensor 7 with a detection range of 10 meters (33 feet) to 150 meters (500 feet).

2. Intruder detector 8 with a detection range from 0.5 meters (1.6 feet) to 15 meters (50 feet).

3. Solar cells 20 for connection to the equipment according to items 1 and 2, suitable for use in the British climate, containing a set of rechargeable batteries and a cyclically interrogated (monitored) radio frequency transmitter.

4. Siren and flashing light unit 9, also with solar cells 18 suitable for use in the British climate and containing a set of rechargeable batteries (modified technology) and a cyclically polling supervised radio frequency receiver.

5. Warning signs (standard equipment).

6. Option: Intruder photo evidence cameras 10 complete with an infrared flash unit connected to the detectors and sensors.

7. Option: Full CCTV camera 12 connected to the detectors.

Internal control equipment (wireless) (See Fig. 8)

1. Control panel 13, expandable to fifteen areas, with a memory computer from which 1000 events can be downloaded, a real-time print output and alphanumeric paging. Cyclic polling (monitored) high-frequency receiver with siren high-frequency transmitter, expandable to 50 signals.

2. Digital LCD keyboard 15, which is backlit .

3. Rechargeable emergency batteries 16.

4. Assembly unit 17 for the control equipment, to form a free-standing portable device 17.

5. Optional real-time printer 14.

6. Optional solar panels suitable for use in the UK climate (if mains power is not available) with rechargeable battery pack.

7. Optional radio frequency signal repeater unit 21 which receives all transmissions from detectors etc. and forwards them to the main receiver 13 (for large construction sites).

WIRED AND WIRELESS SYSTEMS Internal communication facilities (see Fig. 7 and 8) Options

1. High frequency radio unit 22 (0.5 mile range), beep, 4-character or alphanumeric general purpose display (standard equipment).

2. Headlight switching unit 23, which switches or pulses headlights during an alarm activation (standard equipment).

3. External remote digital keypad 24 in a vandal-proof, weatherproof and lockable case (standard equipment).

4. Digital telephone communication link 25 that routes all system events to the 24-hour central monitoring station (standard equipment).

5. Cellular phone data link 26, which relays all system events to the 24-hour central monitoring station and includes rechargeable backup batteries (standard equipment).

6. Intruder photo evidence modem 27 for transmitting several individual images of the intruder to the 24-hour central monitoring station together with the event signal (standard equipment).

7. Full CCTV system for monitoring, recording and transmission, connected to and activated by the detectors (standard equipment).

As described, two new devices have been invented. The intrusion sensor and the intruder detector are discussed below and are preferably designed to meet the stated requirements when used either by themselves or depending on the needs of the configuration of the scaffolding or building together in cooperation (see Fig. 9 and 10). The preferred forms of these detectors no longer have all the inherent operational deficiencies that characterize conventional detectors. The two new detectors together with additional designs and modifications to the existing control, communication and acoustic warning devices result in a unique total system concept. Before describing these devices in detail, it should be mentioned that there are additional applications for complete intrusion detection systems, namely:

1. The entire system can be used to protect the outsides of buildings, walls, billboards and fences, i.e. any boundary above ground where you want to detect a climbing intruder.

2. The complete system may be used to protect external perimeters at ground level or at flat roof level, particularly adjacent to buildings, walls, billboards, fences, etc. or between security fences at least 3.0 metres apart. It is assumed that the ground or subsoil is reasonably level, that it has no plants growing on it and that it does not contain any watercourses or ponds (and that grass is kept to 25 millimetres or less in length) if the system is not mounted sufficiently high above the ground.

3. The entire system can be used in a quick-assembly mode, i.e. mounted on tripods (or free-standing scaffolding poles in concrete foundations). The control devices can then be enclosed in robust weatherproof housings.

Fig. 15 shows a plan view of an intrusion sensor mounted in front of a scaffold surface 3. The figure shows a transmitter 30 and its associated antenna with a large horizontal aperture and a receiver 31 with its associated antenna, which is intended to be identical to the transmitter antenna. The antennas were designed according to the principles in UK 1475111 to significantly reduce the component reflected at the surface. Such a reduction for the practically required Areas can be achieved by reducing the half-power beamwidth of the antennas so that θ/2 is smaller than the angle of incidence α. However, this is not a general statement for all situations. To achieve this, the antennas have large horizontal apertures, thus reducing the beamwidth θ. The apertures are designed to be at least 0.50 meters long in order to obtain a reasonable minimum fence width.

Each antenna is an array of horizontally stacked elements which, at frequencies in the X-band, may be implemented by an array of slot radiators, still assumed to be vertically polarized. The antenna arrays may be any of the embodiments in UK-1475111.

The use of multi-element arrays helps to provide gain to the system and in particular to reduce the horizontal beamwidth. With an arrangement of the type considered, one can easily reduce the half-power beamwidth to 1 degree or less. This is far less than the angle of incidence α of any reflected component over practical ranges, i.e. θ/2 < < α.

The antenna radomes 32 are moved approximately 1 meter towards each other. Their opposite sides are physically closed with a microwave-permeable barrier. This arrangement prevents small animals from entering the area near the antennas where the microwave system would otherwise be vulnerable. They are also extended on their inner sides towards the scaffold surface to close off an area close to the antennas that would not provide a response.

By using large horizontal openings, the system behaviour at different locations becomes much more predictable and, after installation, it becomes much less susceptible to changes caused by plastic sheets and nets. which change the effective value of the antenna length l, or for movements of such tarpaulins and nets which affect l. This considerably reduces the probability of false alarms and there are no dead zones in which the system tends to operate unreliably.

To take advantage of the large horizontal aperture arrays, a block diagram of an intrusion sensor circuit is now described with reference to Fig. 16. In Fig. 16, the transmitter 30 comprises a microwave source 33, such as a Gunn diode or a GaAs FET, and an amplitude modulator 34, which may consist of a multivibrator producing a square wave modulation at a selected frequency in the audio range. The modulated output of the Gunn diode or GaAs FET, such as at X-band, is applied to the antenna 35, which may be an extended array of slotted radiators providing the type of response already discussed, and which is completely enclosed for protection from the weather by the low loss radome 32 through which the X-band radiation is emitted. The transmitter 30 may also be enclosed in the same housing.

The receiver 31 has a similar antenna 36 which feeds a microwave demodulator 37 which recovers the audio modulation. This is followed by a preamplifier 38 and then a filter/amplifier 39 which has a passband at the modulation frequency. The filtered signal is fed to a gain controlled stage 40 which is in an automatic gain control (AGC) loop which operates to provide a substantially long term stable modulation output signal for further processing. The filtered modulation signal is rectified in a detector 41 and provides a DC signal whose level follows the modulation signal level. Part of the DC signal is fed back to the stage 40 as an AGC signal via a time delay circuit 42, for example an RC delay circuit. The delay circuit has a delay of more than one minute. The AGC loop maintains the DC output signal of detector 34 substantially constant with respect to slow changes. Relatively rapid changes in the input signal, such as those caused by the movement of an intruder through the microwave fence between antennas 35 and 36, are not compensated for by the slow-acting AGC loop and appear as corresponding changes in the DC signal of detector 34. The DC signal is applied to a Schmitt trigger 43. A sufficiently large change in the DC level activates the Schmitt trigger and generates an alarm signal.

In a preferred method, an intrusion sensor of the type described is used with a large aperture linear array with circular polarization. Such a microwave array is shown in Fig. 17.

The arrangement 35 or 36 is a slotted waveguide arrangement comprising a solid dielectric waveguide 44, the dielectric core 45 of which is coated with a metal 46, the thickness of which is shown in the figure. Radiating apertures 47 are provided along a wide wall at equal intervals s. These apertures may be circular holes or x-shaped (the term slotted waveguide is used broadly to encompass all aperture shapes). They may be as described in UK-1475111, but the total horizontal aperture may be as small as 0.5 metres.

The radiating apertures 47 are offset to one side from the long axis of the wide wall in order to obtain circularly polarized radiation, see the explanation in the above-mentioned report. The amount of offset is chosen to obtain the best circularity. The mechanism by which circular polarization is obtained is better understood from the following description of a slotted waveguide, see Fig. 19. The waveguide is fed from one side, see the arrow in Fig. 17, and terminates the other side with a matched load 48 to prevent reflections. The sense of the radiated circular polarization depends on the direction of wave propagation in the guide 44. A reflected wave from the other side of the waveguide would easily return the induced circular polarization to a linear polarization.

In addition to terminating the waveguide with a matched load, it is desirable to step the coupling of the apertures 47 to the waveguide 44 to achieve the required power distribution which provides the desired narrow beamwidth of the arrangement.

This allows the arrangement 35 or 36 to be designed to meet the following requirements:

1) the arrangement is not shorter than 0.50 metres;

2) the beam width in the horizontal plane is small and there are no excessive side lobes; and

3) circular polarization.

Finally, the slotted waveguide 44 radiates into a semi-parabolic reflector 49 to reduce the horizontal beam width. This helps reduce reflections from passing vehicles.

Fig. 18 shows a further arrangement 50, again based on the principles given in UK 1475111. The arrangement 50 comprises two parallel waveguide sections 51 and 52 connected in series via a U-shaped section 53. One of the two sections 51 and 52 is fed at the inner end 54. The inner end of the other section is terminated with a matched load 55 for the reasons given above. The waveguide sections may be filled or not and have openings 56, with a distance s between adjacent openings in a waveguide. The openings serve, as already explained, to produce a circular polarization. The radiating apertures 56 in the two parallel sections are offset horizontally. As a result, an aperture in one waveguide section is located horizontally midway between two apertures in the other waveguide and produces circular polarization in the same sense. Detailed information can again be found in UK 1475111.

Fig. 19 shows a slotted waveguide arrangement designed for parallel feeding. However, it can be adapted for series feeding, see the disclosure in UK 1475111.

Fig. 19 shows the center section of a piece of slotted dielectric filled waveguide 60 of rectangular cross-section having radiation apertures 61 in a wide wall. Each aperture is offset by a distance o from the longitudinal centerline G-G of the wide wall. However, unlike the arrangement in Fig. 17, the apertures are not all offset to the same side of the centerline, see the following description.

The arrangement is parallel fed by a feed waveguide 62 which couples into an opening in a narrow wall of the waveguide 60 along the H-H axis. Power supplied in the direction of arrow F enters the slotted waveguide 60, splits equally to the left and right of the H-H axis and propagates along the respective waveguide halves, each of which is terminated with matched loads 63 to prevent reflections. Each half section of the waveguide has the same number of openings 61. The openings are shown as x-shaped slots and the degree of coupling to the waveguide can be controlled by adjusting the slot dimensions.

The mechanism by which circular polarization is obtained is similar to that described in UK-1475111.

It is possible to save equipment by using a single fence that goes around the corners using passive reflectors, see Fig. 20. The passive reflector is preferably a polarization-changing reflector that rotates the polarization of the incident radiation by 90 degrees. With a single reflector, this would of course require that the polarization of the receiver and transmitter antenna arrays be orthogonal, e.g. a stack of vertically polarized elements in one array and a stack of horizontally polarized elements in the other. The advantage of the 90-degree rotated polarization is that unwanted reflections from, for example, a vehicle passing close to the fence are not subject to the 90-degree polarization change and are therefore not answered by the receiver antenna.

One way to avoid the need for different antenna arrangements at the transmitter and receiver is to use a 45 degree inclined polarization of the same design in both arrangements. Such arrangements can of course be cross-polarized if they are directly opposite each other.

One can also use identical antenna arrays with the same horizontal or vertical polarization if the number of polarization changes by 90 degrees along the fence is 2n. An example of this is shown in Fig. 20. There, the boundary line of a rectangular area is protected by a single fence without gaps, using six reflectors 59, each of which rotates the polarization by 90 degrees.

Fig. 9 and 10 show an intruder detector 64, which has yet to be described, and an intrusion sensor 30, 31, which are jointly mounted on a scaffold pole at the outer corner of the scaffold at one end approximately 0.50 meters (1.6 feet) apart. The scaffold is boarded at 5 so that protection for the outer side 3 and the side surfaces 65 is only required on the first level of the scaffold. This can be used to detect an intruder climbing up the exterior surfaces or sides to gain access first to the board area and ultimately to the building. The detection field 66, with an operating range of 10 meters (33 feet) to 150 meters (500 feet), is unaffected by birds and small animals and all external environmental conditions of the scaffold.

The detection fields 67 with an operating range of 0.5 meters (1.6 feet) to 15 meters (50 feet) cover the two endangered side surfaces. The fourth surface 68 coincides with the building; access by climbing is not possible there due to the boards 5.

The intruder detector includes a passive infrared system and a microwave Doppler system. Figure 21 shows in plan and elevation views the infrared detection pattern 70 and the microwave detection pattern 71 in a detection range of 0.5 meters (1.6 feet) to 15 meters (50 feet). Figure 22 shows a narrower detection range. The infrared detection pattern 70 can be quickly adjusted to provide a variable width by rotating the upper and lower lenses in opposite directions. The microwave detection pattern is continuously adjustable in both length and width to accommodate scaffolding changes.

Fig. 23 shows in plan and elevation the intruder detector 64 using the detection pattern attached to the corner of the scaffold 66 and positioned against the scaffold face 3. The infrared detection patterns 70 and microwave detection pattern 71 cover the scaffold side face 65 and detect an intruder 72 climbing onto the board face 5 or beyond. To cover the entire depth, the detection patterns above and below the board face are enlarged to provide front protection when used with or without an intrusion sensor. However, this pattern is above birds and small animals that are standing on the boards 5 or are moving slowly there. If a bird or small animal enters the detection pattern, no alarm is triggered because its speed when flying or jumping through the pattern triggers the pre-trigger and thus prevents a false alarm.

Fig. 24 shows in plan and elevation views the intruder detectors 64 placed in front of the scaffold 66 to create a detection pattern covering the front face 3 at the level of the board plane 5. The microwave detection pattern 71 and the passive infrared detection patterns 70 obviously provide complete coverage.

Fig. 25 shows in plan and elevation views that a reflective active infrared beam transceiver 73 is incorporated into the device to prevent the detector 30 from being covered and intentionally misaligned when the system is armed or turned off. When the infrared beam transceiver 73 is mounted on the corner of the frame 66 and in front of the front 3 at the level of the board area 5, it generates an infrared beam 75 which a reflector 76 reflects back to the transceiver. Should an intruder intentionally cover or misalign the device, the infrared beam 75 is no longer reflected and an alarm signal is given.

The active infrared alignment system can be replaced by an electronic rangefinder or a laser or a light source device.

These devices or the active infrared alignment systems can be attached to the intrusion sensors if required. Alternatively, one or more passive infrared devices can be attached to the intrusion sensors.

In locations with low security risk, if necessary, the intruder detector can be used without the active infrared alignment system or any anti-tamper device and/or without the microwave transceiver.

Finally, Fig. 26 shows the operation of the intruder detector with the help of a block diagram that explains the functions involved themselves. In overview, responses from three detectors are stored. If all responses occur within an adjustable time period, an alarm is triggered. The time period can be adjustable up to 15 seconds for the infrared curtains and higher for the microwave transceiver to allow the alarm to last longer and allow both infrared curtains to be triggered. The adjustable time period is variable to accommodate the type of scaffolding covered and to take into account the climbing speed of the intruder. The pre-trigger resets if a bird or small animal passes by and only triggers the storage timer if the intruder remains in the pattern for a pre-set time period.

Claims (41)

1. A method of installing an intruder alarm system that enables the detection of an intruder climbing through a zone to be protected, the method comprising installing on opposite sides of the zone a microwave transmitter (30) having an associated microwave antenna (35) and a microwave receiver (31) having an associated microwave antenna (36), the receiver (31) being adapted to receive radiation transmitted by the transmitter (30), the receiver (31) having a device responsive to the change in the received radiation outside a predetermined range and generating a signal indicating the presence of an intruder in the zone between the antennas, the transmitter and receiver antennas (35, 36) each having an opening that is not less than 0.50 meters in a direction substantially perpendicular to a vertical surface, the method further comprising mounting the antennas (35, 36) near the vertical surface on opposite sides of the zone to be monitored for the presence of an intruder such that a microwave beam pattern between the antennas (35, 36) provides a detection field extending in a substantially horizontal surface oriented such that the system can detect an intruder climbing through the zone. 2. Method according to claim 1, wherein the horizontal opening of both the transmitter and receiver antennas (35, 36) is 1.5 meters. 3. A method according to claim 1 or 2, wherein each of the antennas (35, 36) has a half-power beamwidth in the horizontal plane of not more than 2 degrees. 4. Method according to claim 1, 2 or 3, wherein the operating frequency of the microwave transmitter (30), the receiver (31) and the associated antennas (35, 36) is in the X-band or K-band range of the spectrum. 5. A method according to any one of the preceding claims, wherein both the transmitter antenna (35) and the receiver antenna (36) contain a horizontal arrangement of radiator elements. 6. A method according to claim 1, wherein each of the antennas (35, 36) includes an array of radiating elements extending in a horizontal plane and cooperating to provide a substantially horizontal beam pattern having a beam half-width of no more than 2 degrees, and the antennas (35, 36) are mounted in spaced relation to one another in the vicinity of the vertical surface so that each element of the receiver array receives radiation components directly from each element of the transmitter array, together with components reflected from the vertical surface from at least some elements of the transmitter array, and the direct components and the surface components add vectorially at the receiver antenna. 7. The method of claim 5 or 6, wherein both the transmitter antenna (35) and the receiver antenna (36) contain a slotted waveguide arrangement (44, 50, 60). 8. The method of claim 7, wherein each slotted waveguide (44, 50, 60) is filled with a dielectric material, and the closest adjacent slots in the array are spaced apart by one wavelength in the waveguide, and the dielectric constant of the dielectric material is such that the absolute spacing equal to one wavelength in the waveguide is a distance between closest adjacent slots in the Range of half to one wavelength in free space. 9. A method according to any one of the preceding claims, wherein both the transmitter antenna (35) and the receiver antenna (36) are circularly polarized. 10. A method according to claim 7 or 8, wherein in each slotted waveguide arrangement (44, 50, 60), each slot thereof is offset from the longitudinal axis of the waveguide wall in which the slot is formed to provide circular polarization. 11. The method of claim 10, wherein each slotted waveguide assembly (44, 50, 60) has a feed opening located substantially centrally along the waveguide for center feeding of the waveguide assembly, and the slots located on one side of the feed opening are located on one side of the longitudinal axis of the waveguide wall in which they are formed, and the slots located on the other side of the feed opening are located on the other side of the longitudinal axis of the waveguide wall. 12. The method of claim 11, wherein the waveguide (44, 50, 60) has a rectangular shape and the feed opening is located in a narrow wall of the waveguide so that the slotted waveguide arrangement is fed in parallel, and the distance between the feed opening and the first slot on one side of the feed opening in the dielectric material filled waveguide is one-half wavelength greater than the distance between the feed opening and the first slot on the other side of the feed opening. 13. The method of claim 11, wherein the waveguide (44, 50, 60) has a rectangular shape and the feed opening located in a wide wall of the waveguide so that the slotted waveguide arrangement is fed in series, and the first slot on one side of the feed opening and the first slot on the other side of the feed opening are equidistant from the feed opening. 14. A method according to any one of claims 11 to 13, wherein the ends of the slotted waveguide (44, 50, 60) are terminated with a matched load to prevent reflections at the waveguide ends. 15. A method according to any one of the preceding claims, wherein the system is installed on a scaffold (3, 4, 5) and the transmitter (30) and receiver (31) are mounted horizontally on either side of the front of the scaffold (3, 4, 5) at a first boarded level to be monitored for the presence of an intruder. 16. A method according to any one of claims 1 to 14, wherein the system is installed on a scaffold (3, 4, 5) adjacent to a wall, and the transmitter and receiver antennas (35, 36) are arranged substantially horizontally, and a further or more further microwave transmitter/receiver pairs (30, 31) are arranged parallel to the first-mentioned transmitter (30) and receiver (31), between the first-mentioned transmitter (30) and receiver (31) and the wall, to extend the detection area (66) and avoid empty spaces through which one can climb and to reduce the effects of surface reflections from the scaffold surfaces and any wooden boards, plastic sheets and/or netting that may be present. 17. A method according to any one of the preceding claims, wherein to protect against false alarms generated on the antennas by birds, melting ice, melting fallen snow, heavy rain, e.g. tropical rains which have antennas (35, 36) radomes (32) whose front surfaces are positioned 0.5 to 1 meter in front of the transmitter and receiver antennas. 18. The method of claim 17, wherein the front sides of the radomes (32) are closed with devices that allow microwaves to pass through. 19. A method according to any one of the preceding claims, wherein the antennas (35, 36) mounted adjacent to the vertical surface are installed above the base of the vertical surface. 20. The method of claim 19, wherein the antennas (35, 36) mounted adjacent to the vertical surface are installed at least half a meter (20 inches) above the base of the vertical surface. 21. A method according to claim 20, wherein the vertical surface is associated with a framework structure (3, 4, 5) having at least a first boarded or unboarded plane, and wherein the antennas (35, 36) are mounted adjacent to the vertical surface at approximately a height determined by the first boarded plane. 22. A method of installing an intruder detection system enabling detection of an intruder climbing through a zone to be protected, the method comprising installing first and second passive infrared devices, each device providing a set of detection pattern segments defining a first curtain (70) and a second curtain (70) respectively, such that their respective curtains (70) extend across the zone being monitored for the presence of intruders, each along vertically spaced, substantially horizontal planes, the system further comprising means responsive to said passive infrared devices, and said responsive means including timing means storing the time at which an intrusion into one of said curtains (70) is detected by the associated passive infrared device and operable to generate an alarm condition signal if an intrusion into the other of said curtains (70) is detected by the other associated passive infrared device before a given time interval has elapsed after the time of the first-mentioned intrusion. 23. The method of claim 22, wherein a microwave transceiver is attached to one or both of the infrared devices, and the microwave transceiver has a detection pattern (71) that overlaps or is at least coextensive with the curtain (70) of at least one infrared device. 24. A method according to claim 22 or 23, wherein the system includes a device for varying the given time interval. 25. The method of claim 22, 23 or 24, wherein the system is operable to set the given time interval to be approximately 15 seconds in duration or less. 26. A method according to claim 22, 23, 24 or 25, wherein the responding means are operable to generate an alarm condition signal if an intrusion into the other of the curtains (70) is detected by the other associated passive infrared device before the given time interval has elapsed and after a further given time interval has elapsed from the stored time of the first-mentioned intrusion. 27. The method of claim 26, wherein the system further includes a device for varying the further given time interval. 28. A method according to claim 26 or 27, wherein the system is operable to set the further given time interval to be approximately 3 seconds in duration or less. 29. A method according to any one of claims 22 to 28, wherein the system further comprises an active alignment device (73, 76) having a transceiver (73) containing a transmitter that transmits an alignment beam (75) and a receiver that detects a reflected component of the alignment beam (75), and the active alignment device is physically attached to either the microwave transceiver or the passive infrared device such that if the passive infrared device or the microwave transceiver to which the alignment device is attached is misaligned, the alignment beam will no longer be reflected back to the receiver of the alignment device, thus providing a safeguard against masking and deliberate misalignment. 30. A method of installing an intrusion detection system that enables the detection of an intruder climbing through a zone to be protected, the method comprising the installation of: a passive infrared device providing a set of detection pattern segments defining a curtain (70), the device being installed so that the curtain (70) extends along a substantially horizontal plane; a microwave transceiver attached to the infrared device such that a detection pattern (71) of the transceiver overlaps the infrared curtain (70) or has at least substantially the same extent; and an active alignment device (73, 76) comprising a transceiver (73) containing a transmitter transmitting an alignment beam (75) and a receiver, which detects a reflected component of the alignment beam (75), and the active alignment device is physically attached to either the microwave transceiver or the passive infrared device, so that if the passive infrared device or the microwave transceiver is misaligned, the alignment beam is no longer reflected back to the receiver of the active alignment device, thus providing a safeguard against masking and deliberate misalignment. 31. The method of claim 29 or 30, wherein the system further comprises a reflector (76) that reflects the alignment beam (75) back to the alignment device, and the reflector (75) is installed so that it is located in the infrared or microwave detection patterns (70, 71) remote from the alignment device. 32. A method according to any one of claims 29 to 31, wherein the transmitter of the alignment device is an infrared beam transmitter. 33. A method according to any one of claims 29 to 32, wherein the system also includes a test circuit device operable to carry out a test of the alignment of the system by means of the alignment device, both in the operative state and in the locked state of the system. 34. The method of claim 33, wherein the test circuitry is configured to test system alignment when the system is to be made operational, and to allow the system to be enabled for operation only if the test indicates that the system is aligned. 35. A method according to claim 33 or 34, wherein the test circuit device is designed to be operative remains after the system has been made operational and placed in an operational state. 36. A method according to claim 33, 34 or 35, operable such that, when the system is in an operational state, obscuring or misaligning the alignment beam for more than 10 to 20 seconds creates a full alarm condition. 37. A method according to any one of claims 22 to 36, wherein the microwave transceiver, if present, the or each passive infrared device and the alignment device, if present, are all housed in one device and enclosed in a common housing. 38. The method of claim 37, wherein the housing is protected against unauthorized intervention by a circuit. 39. A method according to any one of claims 22 to 38 in combination with a method according to any one of claims 1 to 21. 40. A method according to any one of claims 1 to 21, wherein the system is attached to a passive infrared device that provides a set of detection pattern segments that define a curtain (70) such that the curtain (70) extends along a horizontal plane. 41. A method according to any one of claims 1 to 21, wherein the system is attached to a microwave transceiver having a detection pattern (71) that overlaps or at least has the same extent as the detection pattern of the system.